Method and apparatus for determining blood pressure and cardiovascular condition

ABSTRACT

A method is disclosed for determining the blood pressure of a patient. The method includes the steps of affixing a non-invasive pressure inducing device and transducer to the patient. A data stream is obtained from the transducer. The data stream includes pressure data and pulsation signal data. The data stream is processed to create an information stream which correlates the pressure data and the pulsation signal data. The information stream includes at least two pulse maximum points and at least one pulse minimum point. At least one of the systolic, diastolic and mean arterial pressures of the patient are determined by choosing a pressure determination point in the information stream between the two pulse maximum points. Additionally, an apparatus for determining blood pressure is disclosed.

BACKGROUND OF THE INVENTION

The present invention relates generally to a method and apparatus fordetermining blood pressure and more particularly to a non-invasivemethod and apparatus for determining blood pressure, and for providingthe medical practitioner with information about the operation of thecardiovascular system of a patient.

One test often performed on patients by medical practitioners is a testto determine the blood pressure of the patient. Blood pressure is testedoften because a knowledge of a patient's blood pressure provides anoverall reflection of the functioning of his heart and circulatorysystem.

The blood pressure in a patient's arterial system is represented by thepeak systolic and diastolic levels of the pressure pulse and is modifiedby cardiac output, peripheral arteriolar resistance, distensibility ofthe arteries, amount of blood in the system, and viscosity of the blood.Accordingly, changes in blood pressure reflect changes in thesemeasurements. For example, the decrease in vessel distensibility in theelderly lowers diastolic pressure and increases systolic pressure toproduce systolic hypertension. Increases in blood volume may raise bothsystolic and diastolic components.

Normal blood pressure in the aorta and large arteries, such as thebrachial artery, varies between 100 and 140 millimeters of mercury mm Hgsystolic and between 60 and 90 mm Hg diastolic. Pressure in the smallerarteries is somewhat less, and in the arterioles, where the blood entersthe capillaries, it is about 35 mm Hg. However, a wide variation ofnormal blood pressure exists, and a value may fall outside the normalrange in healthy adults. The normal range also varies with age, sex andrace. For example, a pressure reading of 100/60 may be normal for oneperson but hypotensive for another.

Arterial blood pressure can be measured directly or indirectly. The mostcommon known method for measuring blood pressure indirectly is with asphygmomanometer and stethoscope. The primary benefits of thesphygmomanometer and stethoscope procedure are that it is simple for themedical practitioner to use, is non-invasive and is relativelyinexpensive. The sphygmomanometer and stethoscope are often sufficientlyinexpensive to make their cost well within the reach of consumers whodesire to perform blood pressure tests at home. The primary drawback ofthe use of the sphygmomanometer and stethoscope procedure resides in thelimited amount of data that it provides, and the relative inaccuracy ofthe procedure.

The procedure by which a sphygmomanometer is utilized to determine bloodpressure is relatively simple. A collapsed, inflatable blood pressurecuff is affixed snugly and smoothly to a patient's arm, with the distalmargin of the cuff at least 3 cm above the anticubital fossa.

Pressure in the cuff is then rapidly increased to a level of about 30 mmHg above the point at which the palpable pulse disappears. As the cuffis deflated, observations may be made either by palpation orauscultation. The point at which the pulse can be felt is recorded fromthe manometer as the palpatry systolic pressure.

The ausculatory method is usually preferred to the technique describedabove. With this method, vibrations from the artery under pressure,called Korotkoff sounds, are used as indicators.

To determine blood pressure using the ausculatory method, the bell ordiaphram of a stethoscope is pressed lightly over a brachial arterywhile the cuff is slowly deflated. The pressure readings begin at thetime the Korotkoff sounds first become audible. As the cuff is deflatedfurther, the sounds become louder for a brief period. The sounds thenbecome muffled and finally disappear. The systolic blood pressure is thepoint at which the Korotkoff sounds become audible, and the diastolicblood pressure is the point at which the sounds cease to be heard. Thetraditional manual sphygmomanometer may provide inaccurate bloodpressure measurements because it relies too much on human hearingsensitivity and the experience of the operator.

In addition to the "manual" method described above for indirectlymeasuring blood pressure, several electronic devices exist which measureblood pressure according to the same theory as discussed above. One ofthese devices is the MARSHALL ASTROPULSE 78 Model blood pressuremeasuring device which is manufactured by the Marshall MedicalCorporation of Lincolnshire, Illinois.

One problem with the electronic methods discussed above is that they donot provide very accurate measurements of blood pressure.

Electronic devices may not be able to measure all patients' bloodpressure accurately because electronic devices usually depend upon somepre-assumed signal conditions for determining blood pressure. Forexample, female patients typically have a thicker fat layer than malepatients. This thicker fat layer can lead to a less accurate bloodpressure measurement in female patients.

Another difficulty encountered with the above-described indirect bloodpressure measurement techniques is that they only provide a ratherlimited amount of information. Specifically, they do not providesignificant information relating to the dynamics of the cardiovascularsystem of the patient, such as information relating to the volume ofblood flowing through the cardiovascular system and the operation of thevalves of the heart.

Another method for measuring blood pressure is by a direct measurementtechnique. In a direct measurement of arterial blood pressure, a needleor catheter is inserted into the brachial, radial, or femoral artery ofthe patient. A plastic tube filled with heparinized saline solutionconnects the catheter to a pressure sensitive device or a strain-gaugetransducer. The mechanical energy that the blood exerts on thetransducer's recording membrane is converted into changes in electricalvoltage or current that can be calibrated in millimeters of mercury. Theelectrical signal can then be transmitted to an electronic recorder andan oscilloscope, which continually records and displays the pressurewaves.

This direct measurement technique is more accurate than the indirectsphygmomanometer method, and yields an electrically integrated meanpressure. However, as will be appreciated, the direct measurementtechnique has several drawbacks. The invasive nature of the techniquemakes it more difficult for the practitioner, as well as lessconvenient, and more traumatic for the patient.

One other method for indirectly measuring blood pressure is disclosed inGeddes, et al., "The Indirect Measurement of Mean Blood Pressure in theHorse," THE SOUTHWESTERN VETERINARIAN, Summer, 1970, p. 289-294. TheGeddes article describes the indirect measurement of blood pressurethrough the oscillometric method.

The oscillometric method is concerned with the amplitude of theoscillations communicated to a cuff encircling a body member containinga suitably large artery. During deflation of the cuff from abovesystolic pressure, a sequence of oscillations on the cuff-pressureindicator can be seen. At suprasystolic pressure, small oscillations incuff pressure are evident. When cuff pressure falls just below systolicpressure, the amplitude of the oscillations increases. With continueddeflation of the cuff, the oscillations grow in amplitude, reach amaximum, and then decrease continually until the cuff pressure dropsbelow the diastolic pressure of the patient. Currently, severaldigital-display electronic blood pressure monitors are commericallyavailable which utilize the oscillometric method. One such commericallyavailable device is the NORELCO® brand HC-3001 Model home use bloodpressure measuring device which is manufactured by the North AmericanPhillips Corporation of Stamford, Connecticut.

The Geddes article also discusses the measurement of mean arterialpressure (MAP). MAP is defined as the average pressure that pushes bloodthrough the circulatory system in the human body. True MAP is not thearithmetic average of systolic and diastolic pressure, but ratherdepends on the height and contour of the arterial pressure wave. TrueMAP is dependent upon a patient's Cardiac Output (CO) and the TotalPeripheral Resistance (TPR) of the patient's cardiovascular system. Dueto this relation, the equation

    MAP=(CO) (TPR)

is often used by medical practitioners to describe MAP.

MAP is believed by many practitioners to be the most importantmeasurement of blood flow through the circulatory system. It isessential for a practitioner to know the patient's MAP when decidingwhether to prescribe medicines for the patient to control hypertension.For a further discussion of MAP determinations, see the Geddes article.

The device described in Geddes consists of a battery operated electronicoscillometer which displays cuff pressure and the oscillations in cuffpressure. Within the device is a pressure transducer, an amplifier and arapidly responding meter which displays only the amplitude of theoscillations in cuff pressure. A gain control is provided to adjust theamplitude of the display of the oscillations. Additionally, anauxilliary output jack is provided to permit the oscillations to berecorded on a graphic recorder. Geddes utilized the oscillometerdiscussed above simultaneously with a direct pressure measuring deviceon the same animal at the same time to compare the accuracy of hisindirect measurements with the direct measurements. Geddes found thathis indirect oscillation method was not as accurate as the directmethod, with the average ratio of indirect to direct pressure beingabout 0.92:1.

Another indirect method and apparatus for measuring blood pressure isdescribed in Ramsey U.S. Pat. Nos. 4,360,029 and 4,349,034. The '029 and'034 patents are related, and disclose generally identical subjectmatter.

The Ramsey patents relate to an automatic indirect blood pressurereading method and apparatus which automatically and adaptively pump upan arm cuff. The cuff is pumped to a proper pressure by taking theprevious cuff pressure measurement and adding approximately 60 mm to theold pressure before beginning measurement of the amplitude of theoscillations in the cuff. Once the amplitude of oscillations at thestarting pressure are measured, the cuff is deflated a determinedpressure increment to a lower pressure. The oscillations at this lowercuff pressure are then measured.

Ramsey requires that the pressure oscillations satisfy a plurality ofartifact detecting tests before a peak oscillation measurement isaccepted as valid. Should an artifact be detected, additionaloscillations are measured until the oscillations tested free ofartifacts. When this integrity test is satisfied or some predeterminedtime interval is exceeded, the cuff is once again deflated a pressureincrement. The apparatus continues in this fashion until maximumamplitude oscillations are obtained at the lowest cuff pressure, whichis indicative of the mean arterial pressure.

Notwithstanding the above discussed advances in the indirect measurementof blood pressure, room for improvement exists. It is therefore oneobject of the present invention to provide a method and apparatus formeasuring blood pressure which provides the medical practitioner with amore accurate method of measuring blood pressure, and which provides thepractitioner with information regarding the cardiovascular system beyondthat of mere systolic and diastolic arterial pressures.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method isprovided for determining blood pressure of a patient. The methodcomprises the steps of affixing a non-invasive pressure inducing meansand transducer means to the patient. A data stream is obtained from thetransducer means. The data stream includes pressure data and pulsationsignal data. The data stream is processed to create an informationstream which correlates the pressure data and the pulsation signal data.The information stream includes at least two systolic maximum points andat least one diastolic minimum point. At least one of the systolic,diastolic and mean arterial pressures of the patient are determined bychoosing a pressure determination point in the information streambetween the two systolic maximum points.

Preferably, the method also includes the steps of providing a graphicdisplay means and graphically displaying the information stream.

In accordance with another aspect of the present invention, a method isprovided for determining mean arterial blood pressure of a patient. Themethod comprises the steps of affixing a non-invasive pressure inducingmeans and a transducer means to the patient. A data stream is obtainedfrom the transducer means. The data stream includes pulsation signaldata. The data stream is processed to create an information stream whichincludes pulsation signal data and time data. The patient's systolic anddiastolic pressures are determined. A pressure determination point ischosen in the information stream. The chosen pressure determinationpoint is then utilized along with the determined systolic and diastolicpressures to determine the patient's mean arterial pressure.

In accordance with a third aspect of the present invention, an apparatusis provided for determining blood pressure of a patient. The apparatuscomprises a non-invasive pressure inducing means and a transducer meanswhich are attachable to the patient for providing a data streamincluding a pressure data and pulsation signal data. Processing meansare provided for processing the data to create an information streamwhich correlates the pressure data and the pulsation signal data. Agraphic display means is provided for graphically displaying theinformation stream so created.

One feature of the present invention is that an information streamcomprised of pressure data and pulsation data is provided. From thisinformation stream, an instantaneous point is chosen for determining thepatient's systolic blood pressure, diastolic blood pressure or meanarterial pressure. This feature of using an "instantaneous point" hasthe advantage of enabling the medical practitioner to determinediastolic, and systolic blood pressures and mean arterial pressures moreaccurately than known, prior non-invasive blood pressure determiningtechniques.

Another feature of the present invention is that the apparatus of thepresent invention utilizes a non-invasive pressure determining means,such as a cuff pressure sleeve, sphygmomanometer and transducer. Thisfeature has the advantage of making the blood pressure determinationprocess more convenient for the medical practitioner and less risky forthe patient than invasive pressure determining techniques.

It is also a feature of a preferred embodiment of the present inventionthat a graphic display means is provided for graphically displaying theinformation stream, and a data storage means is provided for storing theinformation stream. The graphic display feature has the advantage ofproviding the medical practitioner with valuable data about theoperation of the heart and circulatory system, such as the operation ofthe valves in the heart. The storage feature has the advantage ofpromoting a proper diagnosis of the patient's condition by enabling themedical practitioner to compare the current condition of the patient'sheart and circulatory system against a prior, stored set of data showingthe conditions of the patient's heart at an earlier date. Through anevaluation of the differences between the prior and current informationstreams, the medical practitioner can better analyze the currentcondition of the patient's heart and better determine whether there isany improvement or deterioration in the patient's condition.

A further feature of the present invention is that it provides twomethods for determining Mean Arterial Pressure. These two methods arereferred to herein as "the midpoint method" and the "mathematicalcalculation method."

It was found by the applicant that both the midpoint method and themathematical calculation method have the advantage of providing moreconsistant MAP results than the maximum pulse amplitude method, which isdescribed in the Geddes article. The midpoint method of the presentinvention determines the patient's MAP by utilizing the cuff pressure,below the systolic pressure, when the pulse cycle minimum reaches themidpoint on the cuff pressure axis between two consecutive arterialpulse signal maximum points. The midpoint method has the advantage ofnot requiring the medical practitioner to predetermine the patient'ssystolic and diastolic pressures. The midpoint method is well-suited foruse in routine blood pressure monitoring situations and in situationswherein a numerical, electronic read-out device having limited memoryand computing capability is employed.

The mathematical calculation method comprises a computation of the meanof a patient's pulsation wave form data. To utilize the mathematicalcalculation method of the present invention, a pressure determinationpoint is chosen at a cuff pressure below the patient's diastolicpressure. To choose a pressure determination point, a point is chosen inthe information stream between a systolic maximum and a diastolicminimum, wherein the rate of change of the cuff pressure data versuspulse signal data changes significantly. The above described point isreferred to as the "deflection point." The deflection point is chosen asa point at which to mathematically calculate MAP because this deflectionpoint represents the point at which the patient's aortic valve isclosed, and thus represents the intrinsic blood pressure at the pointwherein the aortic valve is closed. The point wherein the aortic valveis closed is chosen because it is at this point that the patientexperiences the most long lasting and significant "push" of bloodthrough his circulatory system.

The mathematical calculation method has several advantages over themidpoint method. One advantage is that the mathematical calculationmethod is less sensitive to low frequency noises, such as breathingnoises and body movement noises. These low frequency noises caninterfere with the accuracy of the results of the test. Further, themathematical calculation method can be utilized with cuffless bloodpressure measuring devices.

When the mathematical calculation method is used with cuff devices, theresults are less affected by the design and stability of the cuff.Additionally, the mathematical calculation method provides generallymore consistent and accurate results than the midpoint method. Becauseof the enhanced consistency and accuracy of the mathematical calculationmethod, it is particularly well suited to situations such as surgicalprocedures requiring highly accurate and consistent information. Themathematical calculation method does have some disadvantages (whencompared to the midpoint method) in that the mathematical calculationmethod generally requires the use of a device having greater memory andcomputing capabilities.

Additional features and advantages of the present invention will becomeapparent to those skilled in the art upon consideration of the followingdetailed description of a preferred embodiment exemplifying the bestmode of carrying out the invention as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagramatic representation illustrating the componentsutilized in the instant invention;

FIG. 1A is a sample graphic display of the information stream producedby the instant invention, displaying cuff pressure (uncalibrated) as afunction of time;

FIG. 2 is a sample graphic display of the information stream produced bythe instant invention showing the invention in its first mode displayingoverall arterial pulse data as a function of cuff pressure;

FIG. 3 is a sample graphic display showing the information streamprocessed according to the second mode of the invention, displayingpulse signal as a function of cuff pressure in the systolic pressurerange;

FIG. 4 is a graphic display, similar to FIG. 3, showing pulse signal asa function of cuff pressure in the mean arterial pressure range;

FIG. 5 is a graphic display, similar to FIGS. 3 and 4, showing pulsesignal as a function of cuff pressure in the diastolic pressure range;

FIG. 6 is a graphic display showing information processed according tothe present invention in its third mode, wherein a pulse signal of asingle cycle is displayed as a function of time, wherein the maximumpoint of the pulse is assigned to equal the systolic pressure (asdetermined from FIG. 3) and the minimum point of the pulse is assignedto equal the diastolic pressure (as determined from FIG. 4) toillustrate the existence of the deflection point between the pulsemaximum and the pulse minimum of the pulse cycle;

FIG. 6A is a graphic display illustrating the invention in its thirdmode of operation, wherein a plurality of pulse signals over a tensecond time period are displayed;

FIG. 6B is an expanded view of a portion of FIG. 6A;

FIG. 7 is a graphic display showing information processed according tothe present invention in its fourth mode, wherein pulse signal isdisplayed as a function of time, and wherein the original pulse signal,its first derivative signal and its integration signal are displayed ina range wherein cuff pressure is greater than the systolic pressure ofFIG. 3;

FIG. 7A is a display, similar to FIG. 7, showing the pulse signals of amale person exhibiting hypertension;

FIG. 8 is a display showing information processed according to thepresent invention in its fifth mode, wherein pulse signal is displayedas a function of time, and wherein the original pulse signal, its firstderivative signal and its integration signal are displayed in a rangewherein cuff pressure is less than the diastolic pressure of FIG. 5; and

FIG. 8A is a graphic display, similar to FIG. 8, showing the pulsesignals of a male person exhibiting hypertension.

DETAILED DESCRIPTION OF THE DRAWINGS A. Components

FIG. 1 presents a block diagram illustrating the components whichcomprise the apparatus of the present invention, and which are utilizedin conjunction with the method of the present invention.

The apparatus of the present invention includes a non-invasive pressureinducing means such as cuff 10 for exerting a pressure on a body part,such as the arm. A transducer means 16 is provided for picking up thetotal pressure, including the background pressure and the smalloscillation (pulsation) signals. Typically, the background pressuresignals are picked up as DC signals, and the pulsation signals arepicked up as AC signals. The background pressure signals and pulsationsignals picked up are those signals induced by the cuff 10.

The transducer means 16 converts these signals so picked up into anelectrical signal. A graphic display of the data stream which resultsfrom these signals is shown in FIG. 1A.

Although a wide variety of pressure inducing means can be used, thepressure inducing means preferably comprises an inflatable cuff 10 whichcan be wrapped around a limb of a patient.

Typically, such an inflatable cuff 10 includes a pump means (eithermanually activated or electronically activated) which pumps air into theinterior of the cuff 10 to exert pressure on the body part. An exampleof such a cuff 10 is the cuff supplied with the Norelco blood pressuremonitor Model No. HC-3001 cuff which is manufactured by the NorthAmerican Phillips Corporation of Stamford, Connecticut.

Additionally, most, if not all, commerically available cuffs provided asa part of an oscillometric blood pressure monitoring system can beutilized in conjunction with the present invention, so long as acompatible adaptor is utilized to connect the cuff 10 to the pressuretransducer means 16. Further, with more extensive modification, cuffsdesigned for use with nonoscillometric blood pressure monitoring devicescan also be utilized with the present invention.

Preferably, the cuff 10 should include a pressure stop valve whichpermits the user to maintain a selected, constant pressure in the 20 to200 mm Hg pressure range. The stop valve feature is useful in that itpermits the user to obtain arterial pulse wave forms, and therebyextract additional information about the patient's cardiovascularcondition. Examples of such arterial wave forms are shown in FIGS. 7,7A, 8 and 8A, and will be discussed in more detail below.

The pressure transducer 16 primarily comprises a solid state pressuresensor or similar device which is capable of picking up pressuresignals, and converting these pressure signals into an analog electricalsignal for transmission from the transducer means 16. An example of acommerically available transducer which can operate in conjunction withthe present invention is the pressure transducer supplied with theNorelco blood pressure monitor, Model No. HC-3001, discussed above.

Preferably, the pressure transducer 16 will have a linear response rate,or will have a known correlation between the input pressure received bythe transducer 16 and the output electrical signal (e.g. voltage) sentout by the transducer 16. The linear response or known correlationcharacteristics facilitate the calibration of the transducer 16 againsta standard pressure gauge, such as a mercury pressure gauge.Additionally, the transducer 16 should have a fast response rate and awide frequency response. Preferably, the response rate should be lessthan or equal to 0.001 second, and the frequency of the response rateshould be between about 0.2 hertz and 50 hertz or higher. It has beenfound by the applicant that a fast response rate and a wide frequencyresponse contribute to an accurate determination of the systolic anddiastolic blood pressure, and the mean arterial pressure.

The transducer 16 generates a voltage signal which comprises a generallycontinuous overall pressure data stream 20. The overall pressure datastream 20 is sent in a generally continuous manner to the analog todigital convertor 26. The analog to digital convertor 26 converts theanalog information provided by the transducer 16 into digitalinformation. The analog to digital convertor 26 should preferably have asampling rate of 4,000 samples per second or higher; a resolution of 12bits or better; more than one channel for other multi-purposeapplications; and the capability to convert digital signals to analogsignals for feedback control.

Although the above mentioned qualities are preferred, they may not benecessary since the bit resolution and sampling rate of the final dataacquired depends largely on the software program utilized in conjunctionwith the present invention. Generally, a combination of a softwarepackage and an analog to digital convertor 26 that will provide finaldata acquisition of better than 100 items of data per second is adequatefor the present invention. However, better digitizing resolution in thedata stream 20 is always preferable. An example of an analog to digitalconvertor which will perform the functions necessary for the instantinvention is the Eight Channel, High Speed analog to digital convertor,Model No. DAS-8, which is manufactured by the MetraByte Corporation ofTaunton, Massachusetts.

A digitized pressure data stream 30 is fed from the analog to digitalconvertor 26 to a data processing means such as computer 36. As withdata stream 20, the digitized data stream 30 represents an essentiallycontinuous data stream. The computer 36 should preferably have a fastclock speed (e.g. 4.7 megahertz or faster); a large enough memory tostore the data (e.g. 256 kilobytes or greater); and an easy diskoperation system, such as the IBM® DOS operation system.

It should also be noted that the computing speed and memory sizerequired for performing the tasks of the present invention depend on theparticular software chosen. Thus, with the proper software, the usermight be able to utilize a computer 36 having a smaller memory and aslower clock speed. Generally, a clock speed (e.g., 10,000 Hz) fastenough to achieve a final data aquisition rate of better than 100 databits per second is adequate for the present invention. Further, a memoryof less than 256 kilobytes can be utilized if a graphic program is usedwhich is more simple than the LOTUS® 1-2-3 program utilized inconjunction with the present invention.

Examples of computers 36 which have sufficient clock speed and memory toperform the functions necessary in the instant invention include theIBM® Model PC, PC/XT, and PC/AT computers which are manufactured by theIBM Corporation, and their compatible equivalents. Examples of suchcompatible equivalents can be found in most computer related magazines.

As will be appreciated, the computers 36 described above will notprocess the information of the data stream 20 without proper software toperform the processing. The software utilized in conjunction with thepresent invention should perform several functions.

The first function performed by the software is to control the analog todigital convertor 26, so that the digitized data stream 30 can bereceived by the computer 36. A second function performed by the softwareis to convert the digitalized data stream 30 into ASC II format andstore the data in a data storage means such as a disk 50 so that thedata can be retrieved by a program such as LOTUS® 1-2-3 for further dataprocessing and graphic display. A third function of the software is toreceive and to input total time. This inputting of total time starts theconverting performed by the analog to digital convertor 26 at time zeroon the computer's 36 internal clock, and ends the analog to digitalconverting when the total time is up.

A fourth function performed by the software is to filter out the ACoscillation component of digitized data stream 30, so that a DC pressurecurve of the cuff pressure and a separate AC pulsation stream areobtained. This step need not be performed by the software, as a hardwarefilter can be employed to separate the AC and DC components of thepressure signal obtained from the pressure transducer 16 before the datastream 20 is fed to the analog to digital converter 26.

A fifth function of the software is to calibrate the DC cuff pressurecurve by utilizing a precalibrated factor. This precalibrated factor isa number obtained by comparing the digitized number from the analog todigital convertor 26 to either a standard pressure gauge reading or tothe digital reading of a digital blood pressure monitoring device whichis utilized simultaneously in conjunction with the present invention.The sixth function performed by the software is to perform variousnecessary mathematical calculations, such as integration, derivation,etc.

The software utilized by the applicant in conjunction with the presentinvention comprises a two component software package. The firstcomponent comprises a translation component, and the second componentcomprises a data manipulation and graphic display component.

The translation program comprises a data acquisition program, which waswritten by the applicant to collect data from the data stream 30, and tostore the data in a data storage device such as a disk 50 or hard drive(not shown). The translation component collects the data and translatesit into a form usable by the data manipulation/graphic display componentso that the data manipulation/graphic display component can manipulatethe data into a usable form and display it graphically. The functionsperformed by the translation program are (1) noise filtering to filterout spike noises, (2) fitting the curve to the data points obtained, and(3) calibrating the pressure data to millimeters of Mercury. One exampleof a commerically available translation program which can perform thefunctions necessary to perform in the present invention is the LAB TECHNOTEBOOK data acquisition software program Model LTN-03, which ismanufactured by the MetraByte Corporation of Taunton, Massachusetts.

The data manipulation/graphic display component is a data base programwhich remanipulates the data and graphically displays the data on agraphic display means 42. An example of a data manipulation/graphicdisplay program which functions in conjunction with the presentinvention is the LOTUS® 1-2-3 which is manufactured by LOTUS DevelopmentCorporation of Cambridge, Massachusetts.

The data processing means 36 feeds a generally continuous informationstream 40 to a graphic display means, such as a video screen 42 for thecomputer 36. Alternately, an information stream 44 can be fed to aprinter 46 to construct a permanent record of the information containedin the information stream 44. As will be appreciated, printer 46 alsocomprises a graphic display means. Preferably, the printer 46 usedshould be either a dot-matrix printer or a laser printer having thecapability to display the information stream 44 graphically.

As another alternative, an information stream 48 can be fed to a datastorage means, such as a disk 50 or a hard drive for storage and laterretrieval. Through the use of the data storage means to store the dataproduced by the patient, the medical practitioner can be provided withaccess to current and historical data about the patient.

Although information streams 40, 44, 48 are given three separatedesignating numbers, it will be appreciated that information streams 40,44, 48 all contain essentially the same information.

B. Procedure to Operate the Invention

The following procedure is employed in conjunction with the presentinvention. The cuff 10, is affixed to the patient and operated inaccordance with its usual operating procedures. A generally continuousoverall pressure data stream 20 is derived from the cuff 10 andtransducer 16, respectively, and fed into the analog to digitalconvertor 26. The analog to digital convertor 26 converts the analoginformation of the pressure data stream 20 into a digitalized pressuredata stream 30.

The digitized information contained in the data streams 30, 32 is thenprocessed by the computer 36 to separate the AC component (the pulsationsignal) and the DC component (the cuff pressure signal) from the overallpressure data stream 30 received by the computer 36. Further, thecomputer 36 calibrates the cuff pressure data into units of millimetersof mercury to then create the information streams 40, 44, 48, whereinpulsation signal and cuff pressure are correlated to give pulsationsignal as a function of cuff pressure. Additionally, pulsation signaland time are correlated to give the pulsation signal as a function oftime.

The information in the information streams 40, 44, 48 is then fedrespectively to the video screen 42, printer 46, or disk 50. From thedata so displayed, the systolic, diastolic and mean arterial pressuresof the patient can be determined along with other information about thecardiovascular system of the patient.

A sample graphic display is shown in FIG. 1A which displays theinformation stream 40, 44, 48 produced by the present invention, whereincuff pressure (uncalibrated) is shown as a function of time. The curve49 of FIG. 1A is relevant in that it shows that during the test, thepressure exerted by cuff 10 is decreased smoothly over time. Althoughnot readily apparent from the graph of FIG. 1A, it will be appreciatedby those skilled in the art that the cuff pressure at the beginning of ablood pressure test should be greater than the patient's estimatedsystolic pressure, and the cuff pressure at the end of the test shouldbe less than the patient's diastolic pressure.

FIG. 1A is also relevant in that it shows that the duration of the testwas thirty seconds, and that the rate of decrease of cuff pressure wasgenerally constant during the test. Although the applicant employed a 30second test, a shorter or longer test period could be utilized. The useof a shorter test period would have the advantage of reducing the testtime the patient would need to endure, but would have the disadvantageof reducing the accuracy of the test due to the fewer number ofcollected data points. A longer test would have the advantage ofincreasing the accuracy of the test due to the larger number of datapoints collected. However, the larger number of data points would likelydelay the response time of the computer 36, and could overload thecomputer's 36 ability to handle the data.

A generally smooth decrease in cuff pressure during the test ispreferred as it facilitates the construction and interpretation of thegraphic displays produced by the instant invention. However, in somecircumstances it may be preferrable not to decrease the pressuregenerally linearly.

There are several different manners in which the cuff pressure data,pulsation signal data and the time data so correlated can be processed,depending on the user's preference, and on the information so desired.Presented below are several examples of "modes of operation," along withan explanation of the information produced by these various modes, theuses to which the modes are put, and the value of each mode indiagnosing the condition of the patient.

C. Modes of Operation

1. First Mode. A graphic display is shown in FIG. 2 which illustratesthe operation of the invention in its first mode. In this first mode, acurve 51 is shown wherein the patient's pulse signal is displayed as afunction of cuff pressure. FIG. 2 displays the pulse signal/cuffpressure curve 51 throughout the entire duration of the test, which, inthe present example is thirty seconds. The long time period displayed inthis first mode is useful to the practitioner in that it helps thepractitioner to determine whether any irregularities exist in thepatient's pulse signal. For example, the display will show whether thepatient missed a pulse signal, and whether the patient's pulse signalsare spaced irregularly. A missed pulse signal or irregular spacing ofthe patient's pulse signals may indicate that the patient's heart has aserious functional problem.

Curve 51 includes three primary regions: the systolic region 53, themean arterial region 55, and the diastolic region 57. Although theboundaries of these regions cannot be defined with absolute precision,some generalizations can be made. The systolic region 53 comprises thatportion of curve 51 wherein the arterial pulse signal first begins torise. In curve 51, the systolic region 53 includes the area around apexpoints 54 and 56. The mean arterial region 55 includes the area of curve51 adjacent to the peak arterial pulse signal, which in curve 51 is theportion of curve 51 adjacent to apex point 68.

The diastolic region 57 includes the region wherein the arterial pulsesignal decreases rapidly, and in curve 51 includes the portion of curve51 adjacent to apex points 60, 62. Portions of the systolic region 53,the mean arterial region 55 and the diastolic region 57 of curve 51 areshown in more detail in FIGS. 4, 5, and 6, respectively.

The display of the first mode also provides the practitioner with aquick determination of the patient's systolic pressure, diastolicpressure and mean arterial pressure. The systolic pressure is determinedfrom the display in the following manner. It will be noted that a sharprise in the arterial pulse signal occurs between apex point 54 and apexpoint 56. To determine the systolic pressure, one utilizes the nadirpoint 58 between apex points 54 and 56. One then reads the cuff pressureat nadir point 58 to obtain a quick estimate of the patient's systolicpressure. In the instant example, the cuff pressure at nadir point 58 isapproximately 140 mm Hg.

To determine the diastolic pressure, one utilizes the portion of thecurve 51 where the arterial pulse signal is decreasing. One then looksfor apex points, such as apex points 60, 62 wherein a relatively largedecrease in the arterial pulse signal occurs. The nadir point 64 betweenapex point 60, 62 is chosen, and the cuff pressure at the nadir point 64is utilized as the diastolic pressure. In the instant example, thediastolic pressure of the patient at nadir point 64 is approximately 87mm Hg.

To determine an estimate of the patient's mean arterial pressure fromthe graph of FIG. 2, one utilizes the nadir point 67 following thehighest apex point 68 displayed on the graph. One then reads the cuffpressure at this nadir point 67 to obtain an estimate of the patient'smean arterial pressure, which, in the instant example is about 93 mm.Hg.

2. The Second Mode. A graphic display of the information streams 40, 44,48 obtained through the operation of the present invention in its secondmode is shown in FIGS. 3, 4 and 5. More particularly, FIG. 3 displays aninformation stream wherein the arterial pulse signal is shown as afunction of cuff pressure in the systolic range of the patient; FIG. 4displays an information stream showing the arterial pulse signal as afunction of cuff pressure in the mean arterial range; and FIG. 5displays the arterial pulse signal as a function of cuff pressure in thediastolic pressure range.

The determination of the systolic pressure of the patient according tothe present invention will now be explained with reference to FIG. 3. Itwill be noted that FIG. 3 comprises a graphic display of a portion 69 ofcurve 51 of the generally continuous information stream. The curveportion 69 includes a series of data points such as data points 71,which are separated in time generally by 0.037 second. These data points71 include a series of nadir points, such as nadir points 72, 73, and aseries of apex points, such as apex points 74, 75. Apex points 74, 75,relate to pulse cycle (systolic) maximas in a particular pulse cycle,and the nadir points 72,73 represent pulse cycle minimum points. Forpurposes of this discussion, a pulse cycle is defined as a segment ofthe curve portion 69 between any two apex points, such as the thirdcycle 78, which includes that part of the curve portion 69 between apexpoint 74 and apex point 75. It should also be noted that each cycle,such as fourth cycle 79, includes three portions: a rapidly descendingportion 81, a trough portion 83 and a rapidly ascending portion 85. Therapidly descending portion 81 of each cycle is the interval of the cyclewherein the arterial pulse signal decreases rapidly relative to thechange in cuff pressure. The rapidly descending portion 81 ischaracterized by a wide spacing between points, and in fourth cycle 79includes the interval between apex point 75 and nadir point 88. Thetrough portion 83 of each cycle is the interval of the cycle wherein thechange of arterial pulse signal relative to the change in cuff pressureis generally less than in either the rapidly descending portion 81 orthe rapidly ascending portion 85. The trough portion 83 is characterizedby relatively close spacing of the data points, and in the fourth cycle79 includes the interval between nadir point 88 and data point 89. Therapidly ascending portion 85 of each cycle is the interval of each cyclewherein the arterial pulse signal increases rapidly relative to thechange in cuff pressure. Similiar to rapidly descending portion 81,rapidly ascending portion 85 is characterized by wide spacing betweendata points. In fourth cycle 79, the rapidly ascending portion 85 is theinterval of cycle 79 between data point 89 and apex point 91.

A pressure determination point is chosen from curve portion 69. The cuffpressure at this pressure determination point comprises the systolicpressure of the patient. In curve portion 69 the pressure determinationpoint is the nadir point 72 of the third cycle 78. Nadir point 72 ischosen as the pressure determination point because it meets thefollowing three criteria.

The first criteria met by nadir point 72 is that nadir point 72comprises the nadir point between the apex points 74,75 wherein a largerise occurs in the arterial pulse signals at the apex points (orsystolic maxima).

A second criteria for choosing nadir point 72 is that it comprises thenadir point in the cycle 78, wherein a substantial decrease occurs inthe arterial pulse signals between nadir points 72,73 of adjacentcycles.

The third criteria for choosing nadir point 72 relates to the relativeposition of nadir point 72 in pulse cycle 78. If one were to drawimaginary bisector lines, such as bisectors 80,82 which intersect thecuff pressure axis, and which bisect the respective second cycle 84 andthird cycle 78, one would notice that the nadir point 73 of second cycle84 is positioned generally adjacent to, or on bisector 80. However, itwill also be noticed that nadir point 72 of the third cycle 78 ispositioned to the left of bisector 82 and, in fact, is positioned at theextreme left of the trough portion 83 of the curve portion 69 in thirdcycle 78. In choosing a nadir point to serve as a pressure determiningpoint, one chooses the nadir point 72 of the first cycle (here thirdcycle 78) wherein the nadir point 72 is located at or close to thebeginning of the trough portion 83.

By way of contrast, it should be noted that nadir points 86, 73 of thefirst and second cycle 84, respectively, are located near the center ofthe trough portion, and the nadir points 88,90 of the fourth and fifthcycles are located in a position similar to nadir point 72 at theextreme beginning or leftward most end of the trough portion of therespective fourth and fifth cycles.

Using nadir point 72 as the pressure determination point, one candetermine that the systolic pressure of the patient is 140.0 mm Hg. byreading the cuff pressure at the nadir point 72.

The choice of nadir point 72 has physiological significance. Nadir point72 represents a point on the curve 51 wherein the pulse signal drops toits minimum almost immediately following its prior peak at apex point74. This immediate drop in the pulse signal indicates that the intervalof time between peak 74 and nadir point 72 represents the time at whichthe patients blood pressure overcomes the pressure of the cuff 10 tothereby permit a small amount of blood to flow through the arteriesblocked by the cuff 10. This small amount of blood flow causes thesudden drop in the arterial pulse signal. This sudden drop is reflectedin the graph by the positioning of nadir point 72 at the beginning ofthe trough portion of cycle 78, and is also reflected by the drop inarterial pulse signal between adjacent nadir points 73,72.

The present invention provides a more accurate means for determiningsystolic pressure. As will be appreciated by medical practitioners, anaccurate knowledge of a patient's systolic blood pressure is extremelyuseful in diagnosing a patient's condition. One reason the knowledge ofsystolic pressure is important is that practitioners often utilize asystolic pressure exceeding 140 mm Hg. as a benchmark for determiningwhether a patient is hypertensive.

Determining systolic pressure accurately is not an easy task. Apatient's systolic pressure is the highest pressure point of thecardiovascular system. Difficulty arises in determining systolicpressure since this highest point may only remain for a short period oftime, for example, 0.1 second or less. Due to the short duration of thishighest point, the actual highest point systolic pressure may be missedby a practitioner or a device measuring systolic pressure, because thepractitioner or device are incapable of capturing the systolic pressureat its highest point.

The present invention overcomes many of these problems by betteridentifying the very point at which the patient's blood pressure reachesthis highest point systolic pressure. By better identifying this highestpoint systolic pressure, the present invention provides generally moreconsistent data than that provided by known prior art electronicdevices.

A graphic display illustrating a patient's arterial pulse signal as afunction of cuff pressure is shown in FIG. 4. Specifically, FIG. 4displays the patient's arterial pulse signal and cuff pressure in therange wherein the patient's mean arterial pressure can be calculatedutilizing the "mid-point method" discussed above.

FIG. 4 is similar to FIG. 3 in that it displays a generally sinusoidalportion 100 of curve 51 comprised of a generally continuous series ofdata points separated in time by about 0.037 seconds. Curve portion 100is taken from the mean arterial range 55 of curve 51 and includes aseries of apex points 102,104,106,108,110,112 and a series of nadirpoints 114,116,118,120,122. The apex points 102,104,106,108,110,112 andnadir points 114,116,118,120,122 define a series of five pulse cycles,including a first cycle 126, second cycle 128, third cycle 130, fourthcycle 132, and fifth cycle 134. For purposes of illustration, imaginarybisectors 138,140,142 have been drawn through the respective third cycle130, fourth cycle 132, and fifth cycle 134.

It has been found by the applicant that the patient's mean arterialpressure (MAP) can be determined by reading the cuff pressure from thegraph of the nadir point 120 of the cycle 132 wherein the nadir point120 is positioned at the middle of the trough portion 144 of the cycle132. To clarify this, it should be noted that nadir point 120 interceptsbisector 140 of the fourth cycle 132. It should also be noted that thenadir point 118 of the prior cycle (third cycle 130) falls generally tothe left of bisector 138 and that the nadir point 122 of the succeedingcycle (fifth cycle 134) falls to the right of bisector 142. When onereads the cuff pressure at nadir point 120, one finds that the patient'smean arterial pressure is approximately 93 mm Hg.

It should be noted that the mean arterial pressure determined from FIG.4 (93 mm Hg) is essentially the same as the mean arterial pressure (94mm Hg) estimated from FIG. 2, wherein the maximum amplitude point methodwas utilized. One advantage to the use of the mid-point method over themaximum amplitude method is that the mid-point method is generally notas sensitive to extraneous noises as the maximum amplitude method. Themid-point method is not as sensitive to noises for many of the samereasons that an FM radio signal is normally less noisy than an AM radiosignal.

Although the mid-point method of the present invention does provide anadvance over the maximum amplitude method, the mathematical calculationmethod is likely more accurate than the mid-point method. Themathematical calculation method is likely more accurate because it isless affected by the patient breathing deeply, the interposition of asleeve between the cuff 10 and the body part, and the presence of asignificant fat layer between the arteries and skin layer of thepatient. The mathematical calculation method is discussed below as thethird mode of the present invention.

A graphic display is presented in FIG. 5 which demonstrates thedetermination of a patient's diastolic blood pressure according to thepresent invention. FIG. 5 displays a generally sinusoidal curve portion150 of curve 51, which is comprised of a series of data points separatedin time by about 0.037 second. Curve portion 150 overlaps with curveportion 100 (FIG. 4) insofar as both curve portions 100, 150 share twoapex points 110,112, two nadir points 120,122 and cycle 134. Curveportion 150 also includes apex points 156,158,160 and nadir points164,166,168,170. These apex points 110,112, 156,158,160 and nadir points122,164,166,168,170 define five pulse cycles 134,176,178,180,182.Bisectors 184,186 have been drawn through cycles 176 and 178,respectively, in a manner similar to the bisectors 80,82 of FIG. 3 andthe bisectors 138,140,142 of FIG. 4.

To choose a pressure determination point, one chooses a nadir point 166and reads the cuff pressure (85 mm Hg) at the pressure determining nadirpoint 166. To determine which nadir point to use as the pressuredetermination point, one uses the nadir point 166 which is located at,or adjacent to the end of the trough portion 188 of its respectivecycle. As will be noted from the graph, nadir points 164,168,170 aregenerally not disposed adjacent to the end of their respective troughportions. As discussed in connection with FIG. 4, nadir point 120 isdirectly in the middle of the trough portion of its respective pulsecycle.

Another way of viewing pressure determining nadir point 166 is thatnadir point 166 is at or adjacent to the beginning the portion of cycle178 wherein the arterial pulse signal rises rapidly toward thesuccessive apex point 158. The choice of a nadir point 166 which isdisposed at or near the beginning of the rapidly ascending portion of acycle as a pressure determining point has physiological significance. Anadir point 166 so positioned indicates that the pressure exerted by thecuff 10 is sufficiently insignificant so that the cuff 10 no longerrestricts the flow of blood through the arteries. As will be familiar tomedical practitioners, a patient's diastolic pressure is generallydefined as the pressure at which the pressure exerted by a cuff 10 nolonger restricts the flow of blood.

The applicant found that utilizing this method provides a ratherconsistent and accurate determination of a patient's diastolic bloodpressure.

It is believed by applicant that the reason for this enhancedconsistency and accuracy of the present invention is due to the factthat the present invention better captures the exact arterial pulsesignal point wherein the pressure exerted by the cuff 10 no longerrestricts the flow of blood past the cuff 10. Additionally the accuracyand consistency of the method of the present invention are enhancedbecause the present invention is less affected by external noises thatcan affect the amplification of pulses.

3. Third Mode. A graphic display of the blood pressure determinationmethod of the present invention in its third mode is shown in FIG. 6.The third mode is utilized to determine a patient's mean arterialpressure according to the "mathematical calculation method" of thepresent invention. The graphic display in FIG. 6 shows a single pulsecycle having a plurality of data points connected together to form agenerally sinusoidal curve 200. Curve 200 correlates the arterialpressure of the patient as a function of time, with arterial pressurebeing displayed on the Y axis, and time being displayed on the X axis.Although cuff pressure is not shown in curve 200, the cuff pressureresponding to curve 200 is a cuff pressure lower than the patient'smeasured diastolic pressure. The reasons for choosing a cuff pressureless than diastolic pressure will be explained in more detail below.

The graphic display shown in FIG. 6 is constructed in the followingmanner. A single pulse cycle is utilized at a cuff pressure lower thanthe patient's measured diastolic pressure. The apex point 202 of thecycle is then set at the patient's measured systolic pressure. In theinstant example, this is 140 mm Hg. The lowest point of the cycle, nadirpoint 204, is then set at the patient's measured diastolic pressure. Inthe instant example, this is 85 mm Hg. Using these two known points, thegraph is then calibrated by linearly interpolating arterial pressuresbetween the measured systolic pressure and the measured diastolicpressure on the graph to create a linear scale of arterial pressures.

It is apparent that the mean arterial pressure should be somewherebetween the patient's systolic and diastolic pressures. A pressuredetermination (deflection) point 206 is chosen because it meets thefollowing criteria: first, when measuring mean arterial pressure, thepressure determination point is a point on the curve 200 wherein thepatient's arterial pressure is decreasing with time. In other words, thepressure determination point 206 will be somewhere between the pulsemaxima (apex point 202) and pulse minima (nadir point 204) and not at apoint between the pulse minima (nadir point 204) and the pulse maxima ofa succeeding cycle.

The second criteria met by pressure determination point 206 is that itrepresents a point wherein the rate of change of arterial pressure vs.time changes significantly. When viewing the graph, this change isrepresented by a change in the slope of curve 200, wherein the slope ofthe curve 200 increases significantly. As shown in FIG. 6, the slope ofthe portion of curve 200 between apex point 202 and pressuredetermination point 206 is approximately minus 225 mm Hg per second,whereas the slope of the portion of curve 200 in the interval betweenpressure determination point 206 and nadir point 204 is approximatelyminus 40 mm Hg per second. Thus, it will be noticed that betweenpressure determination point 206 and nadir point 204, the slope of curve200 increases significantly, although still remaining negative. Althoughthe slope of the portion of the curve between the pressure determinationpoint 206 and the nadir point 204 remains negative, the applicant hasfound that occasionally the slope of the curve will become positive fora short interval of this portion, such as between pressure determinationpoint 206 and the two or three points which follow pressuredetermination point 206. It will be appreciated by those familiar withcalculus that pressure determination point 206 can also be described asa point wherein the first derivative of curve 200 changes significantlyor a point wherein the rate of change in the slope of curve 200 reachesa maximum in the interval between apex point 202 and nadir point 204.

The applicant has found that the use of a "deflection point," such aspoint 206, as a pressure determination point, yields quite consistentresults in the measurement of the patient's mean arterial pressure. Oneexperiment utilized by applicant to prove the consistency of thismathematical calculation method as an accurate and consistent determinorof mean arterial pressure is shown in FIGS. 6A and 6B.

FIG. 6A shows a series of pulse cycles shown on a graph wherein arterialpulse signal is shown as a function of time. In the graphs of FIGS. 6Aand 6B, the arterial pulse signal equals zero (Y=0) line, is set toequal the mathematical true mean value of all pulsation signalsdisplayed on the respective graphs. Another way of expressing this isthat the area under entire curve 209 (FIG. 6A) equals the area of arectangle defined by points A, B, C and D, which of course equals thearea of the graph under the Y=0 line.

FIG. 6A shows a curve 209 of twelve pulse cycles recorded over a periodof approximately ten seconds at a cuff pressure between 50 and 40 mm Hg.As will be appreciated, a cuff pressure of 40-50 mm Hg is less than thepatient's diastolic pressure, which is typically around 80 mm Hg. Itwill be noticed that the pressure determining deflection points 210 ofeach cycle tend to hover around the Y=0 line, thus proving that thedeflection point does accurately reflect the mean arterial pressure ofthe patient.

FIG. 6B is an expanded view of the first three cycles 212,214,216 shownin FIG. 6A. This expanded view illustrates more clearly that pressuredetermining deflection points correlate well between each other aroundthe Y=0 line, and are not easily affected by other unknown oscillationnoises. This fact is important in that it enables the present inventionto provide a more precise method of determining mean arterial pressurethan other known methods.

It should be noted that the precision by which the mathematicalcalculation method of the present invention determines mean arterialpressure is dependent upon an accurate determination of both systolicand diastolic pressures. This accurate determination is provided by thepresent invention and is described in conjunction with FIGS. 3 and 4above.

The applicant has found that the mean arterial pressure is best measuredat a cuff pressure less than the patient's diastolic pressure. At apressure less than the patient's diastolic pressure, the cuff 10 andtransducer 16 are utilized primarily as sensing devices to pick up thepulsation signal of the patient's arteries. When using apressure-sensing or pulsation sensing device, such as an ultrasonic oroptical transducer to pick up and record the arterial pulse signals, itis expected that one will achieve the same correlations between thepressure determination deflection point, the apex point, and the nadirpoint as are achieved through the use of a cuff 10 device. Thesimilarity of these correlations permits a cuffless blood pressuremeasuring device to be utilized to provide accurate determinations ofthe patient's mean arterial pressure, so long as the patient's systolicand diastolic pressures are obtained by relatively accurate measuringdevices.

Another feature of the present invention is that if the practitioner hasknowledge of the manner in which the mean arterial deflection point, thesystolic maximum apex point and the diastolic minimum nadir point arecorrelated, it is possible for the practitioner to determine any of thethree points by knowing only two of the points. For example, if oneobtains a patient's arterial pulse signal, diastolic pressure and meanarterial pressure, the practitioner can then calculate the patient'ssystolic pressure.

The determination of the patient's mean arterial pressure is a veryimportant for enabling the practitioner to treat the patient properly.As discussed above, the patient's mean arterial pressure is generallyequal to the patient's cardiac output times the total peripheralresistance of the patient's cardiovascular circulatory system. Incontrolling a patient's hypertension, the practitioner can choose eitherto control the patient's cardiac output by prescribing one type ofmedicine, or controlling the patient's total peripheral resistance byprescribing another type of medicine. It is important for a practitionerprescribing such medicine to have an accurate reading of the patient'smean arterial pressure to determine the correct dosages of such medicineto administer.

4. Fourth Mode. FIG. 7 comprises a graphic display showing the presentinvention's fourth mode wherein data relating to arterial pulse waveforms is displayed as a function of time. The primary purpose of thefourth mode is to gather information about the condition of thepatient's cardiovascular system, rather than determining the patient'sblood pressure. Three curves are drawn on FIGS. 7 and 7A.

In FIG. 7, the first curve 240 comprises a series of data pointsconnected together by the curve 240. The data points correspond to anarterial pressure pulse signal which, in the instant example, ismeasured at a cuff pressure greater than the patient's systolicpressure. The second curve, first derivative curve 244, is a curvecomprising the first derivative of the arterial pulse signal curve 240.The third curve 248 comprises the integration of the arterial pressurepulse signal curve 240 over the duration of the portion of curve 240shown in the graph.

FIG. 7A contains three similar curves including an arterial pressurepulse signal curve 250, a derivative curve 252 which is the firstderivative of arterial pressure curve 250, and an integration curve 254which is an integration of the arterial pressure curve 250. FIG. 7displays arterial pulse wave forms for a person with a normalcardiovascular condition, whereas FIG. 7A displays arterial pulse waveforms of a patient exhibiting hypertension. The patient whose arterialpulse wave forms are shown in FIG. 7A was found to have a measuredsystolic pressure of 158 mm Hg, a diastolic pressure of 80 mm Hg, and amean arterial pressure of 105 mm Hg. As will be appreciated by thoseskilled in the medical art, a systolic pressure of 158 mm Hg is abovenormal.

It should also be noted that although the information shown in FIGS. 7and 7A were obtained during a "test" wherein the cuff pressure wasdecreasing over time, this need not be the case. It is possible toobtain the information neded for the invention's fourth and fifth modesby maintaining a constant cuff pressure.

Comparing FIGS. 7 and 7A, one will note that several differences existbetween curves 240,244,248 and curves 250,252,254. These differences areindicative of the hypertensive condition of the patient of FIG. 7A. Thefirst difference between the two sets of curves is that the curves250,252,254 of the hypertensive patient (FIG. 7A) are noisier than thecurves 240,244,248 of the normal patient (FIG. 7). A second differencebetween the two sets of curves is that the arterial pressure pulse curve250 of the hypertensive patient includes splits or dips such as at 256.These splits or dips 256 are absent in the arterial pulse pressuresignal curve 240 of the normal patient. These splits or dips 256 arealso reflected in the first derivative curve 252 of the hypertensivepatient as deflection points 258 in the first derivative curve 252. Thethird difference between the two curves is that in the arterial pulsecurve 250 of the hypertensive patient, the "diastolic" portion of thecurve in each cycle from data point 260 to data point 262 rises to ahigher level than the corresponding diastolic portion (from point 264 topoint 266) of the arterial pulse curve 240 of the normal patient.

Several reasons exist for utilizing arterial pulse curves which aretaken at a cuff pressure above the patient's systolic pressure. Onereason for using a suprasystolic cuff pressure is that when the cuffpressure is greater than the systolic pressure, the patient's arterialvessels in the arm are blocked at the cuff 10 location. With suchblockage, the blood vessels work as a signal transfer line whichtransmit pressure signals from the heart to the aorta, and through thearterial blood vessels to the cuff 10, which then picks up the vibrationsignals. Although a vessel filled with blood is not a perfectvibration-conducting medium, the information so obtained should bequalitatively representative of the aorta pressure curve, whichheretofore could only be measured by invasive blood pressure determiningmeans. Additionally, the information so obtained should also reflectother influences such as the characteristics of the arterial vessels andthe cuff 10-to-blood-vessel coupling effects.

Although an interpretation of the wave forms shown in FIGS. 7 and 7A isvery difficult, the wave forms of FIGS. 7 and 7A are useful to thepractitioner when compared to similar prior data from the same patient.When compared to such a prior data, the information of FIGS. 7 and 7Acan provide the practitioner with important information about thecondition of the patient's cardiovascular system, such as thedeterioration of the patient's heart, aortic valve noises, and changesin blood flow due to changes in the patient's blood vessels.

Additional information is provided by the first derivative curves244,252. The first derivative curves 244,252 display the change of slopeof arterial pressure curves 240,250, respectively. As such, the firstderivative curves 244,252 are generally more sensitive to the presenceof low level noises. A display of these low level noises can be used bythe practitioner to help better diagnose noises associated with certaincardiovascular problems. For example, in FIG. 7A many of the smalloscillation noises present in the arterial pulse pressure curve 250 arebetter displayed on the first derivative curve 252. Examples of thesesmall oscillations are splits 256 which are better displayed asdeflection points 258 on the first derivative curve 252.

The integration pressure curves 248,254 are the summation of thepressure signal data from the data collected at the beginning (left) ofthe graph to the last point collected and displayed on the graph. Thus,the information displayed by the integration curves 248,254 relates tothe total accumulated arterial pressure multiplied by time over thecourse of the display. Since the information displayed in FIGS. 7 and 7Awas obtained at pressures above systolic pressure, no blood flowedthrough the body part in area of the cuff 10. The integration of eachpulse therefore provides information about the strength of each strokeof the heart. Although the integration curves 248,254 are difficult tointerpret by themselves, they are useful to the practitioner when usedin conjunction with similar integration curves taken from the patient atan earlier date, to provide information to the practitioner about thecondition of the patient's cardiovascular system.

5. Fifth Mode. The graphic displays shown in FIGS. 8 and 8A set forthdata presented by the invention in its fifth mode. FIGS. 8 and 8A aresimilar to FIGS. 7 and 7A in that both sets of figures show arterialpulse wave forms as a function of time, and are utilized primarily toprovide information about the condition of the patient's cardiovascularcondition rather than for determining blood pressure.

Additionally, both sets of figures contain three curves. FIGS. 8 and 8Aeach include arterial pressure pulse curves 300,302, first derivativecurves 304,306, and integration curves 308,310. The primary differencebetween FIGS. 7 and 7A and FIGS. 8 and 8A is that FIGS. 7 and 7A displayinformation obtained at cuff pressures above the patient's systolicpressure, whereas FIGS. 8 and 8A display information obtained at cuffpressures below the patient's diastolic pressure.

FIG. 8 presents information taken from a male patient having normalblood pressure, and FIG. 8A presents information taken from a maleperson exhibiting hypertension. Several major differences exist betweenthe curves 300,304,308 of the normal person (FIG. 8) and the curves302,306,310 of the hypertensive person (FIG. 8A). First, it will benoticed that more high frequency noises are present on the arterialpulse pressure curve 302 of the hypertensive patient. Examples of suchhigh frequency noises are best shown at points 311,313 of the firstderivative curve 306 of FIG. 8A.

A second difference is the presence of "splits" at the apex of thearterial pulse pressure curve 302 of the hypertensive patient. Althoughno splits are visible on the arterial pulse pressure curve 302 of thehypertensive patient, deflection points 312 on the first derivativecurve clearly indicate the presence of such splits. A third differenceis that the hypertensive curve exhibits significant increases in thediastolic portion of the curve, between points 314,316, similar to thesignificant increase shown in the diastolic portions of the arterialpulse curve 250 between points 260 and 262 of FIG. 7A.

The information displayed in the fifth mode is similar to theinformation displayed in the fourth mode of the present invention. Theprimary difference between the information displayed results from thefact that in the fourth mode (FIGS. 7 and 7A) the cuff pressure at whichthe information is taken is above the patient's systolic pressure.Therefore, in the fourth mode, no blood is flowing past the cuff 10picking up the signals. In the fifth mode, however, the restrictions onthe flow of blood caused by the cuff 10 are minimal so that blood canflow through the area freely.

Theoretically, in the fourth mode (above systolic pressure) with noblood flowing, the cuff 10 measures the strength of the heart strokewhich sends out a pressure signal to the cuff 10, whereas in the fifthmode (below diastolic pressure) the cuff 10 measures the oscillations ofthe arterial circulation system caused by the pressure wave emanatingfrom the heart stroke on the arm where the cuff 10 is placed. Generally,therefore, the fourth mode, with no blood flowing, provides informationabout the strength of the heart contraction. The fifth mode, with theblood flowing without restriction, gives information to the practitionerabout the flow of blood in the circulatory system. Information about thestrength of the heart and the amount of blood flow in the cardiovascularsystem relate directly to the cardiac output and the resistance of thecardiovascular circulatory system respectively. As discussed above,information about cardiac output and the resistance of thecardiovascular system are essential to the practitioner in the diagnosisand treatment of patients having hypertension.

Although the invention has been described in detail with reference tothe illustrated preferred embodiments, variations and modificationsexist within the scope and spirit of the invention as described and asdefined in the following claims:

What is claimed is:
 1. A method of determining blood pressure of apatient comprising the steps of:a. affixing a non-invasive pressureinducing means and transducer means to the patient, b. elevating thepressure induced by the pressure inducing means to a suprasystolicpressure, c. decreasing the pressure induced by the pressure inducingmeans over time to a pressure below diastolic pressure, d. obtaining adata stream from the transducer means, the data stream includingpressure data and pulsation signal data, e. processing said data streamto create an information stream which correlates the pressure data andthe pulsation signal data, the information stream including at least twopulse maximum points and at least two pulse minimum points, and f.examining the information stream to determine at least one of thesystolic, diastolic and mean arterial pressures of the patient byselecting at least one of the at least two pulse minimum points as apoint for determining said at least one of the systolic, diastolic andmean arterial pressure of the patient.
 2. The method of claim 1 whereinsaid at least two pulse maximum points comprise at least two consecutivepulse maximum points and the step of selecting at least one of the atleast two pulse minimum points comprises the step of selecting a pulseminimum point between the at least two pulse maximum points which meetsat least one of the following criteria:(a) the pulse minimum pointoccurs between a pair of consecutive pulse maximum points wherein thefirst pulse maximum point is substantially less than the second pulsemaximum point, and (b) the pulse minimum point occurs between a pair ofconsecutive pulse maximum points wherein the first pulse maximum pointis substantially greater than the second pulse maximum point.
 3. Themethod of claim 1 further comprising the steps of providing a graphicdisplay means and graphically displaying the information stream.
 4. Themethod of claim 3 wherein the step of graphically displaying theinformation stream comprises the step of graphically displaying thepulsation signal data as a function of cuff pressure.
 5. The method ofclaim 3 wherein the step of graphically displaying the informationstream comprises the step of graphically displaying the pulsation signaldata as a function of time.
 6. The method of claim 3 wherein the step ofproviding a graphic display means comprises the step of providing avideo display means.
 7. The method of claim 3 wherein the step ofproviding a graphic display means comprises the step of providing aprinter means.
 8. The method of claim 1 wherein the step of creating aninformation stream comprises the step of creating a generally sinusoidalinformation stream curve, the at least two pulse maximum pointscomprising apex points of the generally sinusoidal information streamcurve, and the at least two pulse minimum points comprise nadir pointsof the generally sinusoidal information stream curve, the generallysinusoidal information stream curve including at least one pulse cycledefined as an interval of the curve between a pair of consecutive pulsemaximum points.
 9. The method of claim 8 wherein the at least one pulsecycle includes a pulsation signal rapidly descending portion, a pulsesignal trough portion and a pulse signal rapidly ascending portion. 10.The method of claim 9 wherein the step of examining the informationstream to determine at least one of the systolic, diastolic and meanarterial pressures by selecting at least one of the at least two pulseminimum points as a point for determining said at least one of thesystolic, diastolic and mean arterial pressures of the patient comprisesthe step of selecting said at least one pulse minimum point as a pointfor determing the systolic pressure of the patient.
 11. The method ofclaim 10 wherein the step of selecting the at least one pulse minimumpoint comprises the step of selecting the pulse minimum point of thepulse cycle wherein the pulse minimum point occurs at the beginning ofthe pulse signal trough portion of the pulse cycle.
 12. The method ofclaim 10 wherein the step of selecting the at least one pulse minimumpoint comprises the step of selecting the pulse minimum point of thepulse cycle wherein the pulse minimum point occurs at the first datapoint of the pulse signal trough portion.
 13. The method of claim 9wherein the step of examining the information stream to determine atleast one of the systolic, diastolic and mean arterial pressures byselecting at least one of the at least two pulse minimum points as apoint for determining said at least one of the systolic, diastolic andmean arterial pressure of the patient comprises the step of selectingsaid at least one pulse minimum point as a point for determining thediastolic pressure of the patient.
 14. The method of claim 13 whereinthe step of selecting the at least one pulse minimum point comprises thestep of selecting the pulse minimum point of the pulse cycle wherein thepulse minimum point occurs at the end of the pulse signal trough portionadjacent to the pulse signal rapidly ascending portion.
 15. The methodof claim 13 wherein the step of selecting the at least one pulse minimumpoint comprises the step of selecting the pulse minimum point of thepulse cycle wherein the pulse minimum point occurs in the pulse signaltrough portion at the last data point of the pulse signal troughportion.
 16. The method of claim 9 wherein the step of examining theinformation stream to determine at least one of the systolic, diastolicand mean arterial pressures by selecting at least one of the at leasttwo pulse minimum points as a point for determining said at least one ofthe systolic, diastolic and mean arterial pressures of the patientcomprises the step of selecting said at least one pulse minimum point asa point for determining the mean arterial pressure of the patient. 17.The method of claim 16 wherein the step of selecting the at least onepulse minimum point comprises the step of selecting the pulse minimumpoint of the pulse cycle wherein the pulse minimum point occurs in themiddle of the pulse signal trough portion of the pulse cycle.
 18. Themethod of claim 16 wherein the step of selecting the at least one pulseminimum point comprises the step of selecting the pulse minimum point ofthe pulse cycle wherein the pulse minimum point occurs at a pressuredata point generally equal to the average of the pressure data points ofthe two pulse maximum points which define the pulse cycle.
 19. Themethod of claim 1 wherein the step of creating an information streamcomprises the step of creating a generally sinusoidal information streamcurve comprised of a series of pulse cycles, each pulse cycle beingdefined by an interval of the curve between adjacent pulse maximumpoints, and each cycle including a rapidly descending portion, a troughportion, a rapidly ascending portion, and the at least one of the atleast two pulse minimum points comprises a point in the trough portion.20. The method of claim 19 wherein the step of examining the informationstream to determine at least one of the systolic, diastolic and meanarterial pressures by selecting at least one of the two pulse minimumpoints as a point for determining said at least one of the systolic,diastolic and mean arterial pressures of the patient includes the stepof selecting a pulse cycle in said series of pulse cycles wherein thepulse minimum point of the pulse cycle occurs adjacent to the beginningof the trough portion of the pulse cycle to determine the systolicpressure.
 21. The method of claim 20 wherein said pulse cycle selectedcomprises the first pulse cycle of said series of pulse cycles whereinthe pulse minimum point occurs adjacent to the beginning of the troughportion, and wherein the systolic pressure is determined by utilizingthe pressure data at the pulse minimum point so chosen.
 22. The methodof claim 19 wherein the step of examining the information stream todetermine at least one of the systolic, diastolic and mean arterialpressures by selecting at least one of the two pulse minimum points as apoint for determining said at least one of the systolic, diastolic andmean arterial pressures of the patient includes the step of selecting apulse cycle in said series of pulse cycles wherein the pulse minimumpoint of the pulse cycle occurs adjacent to the end of the troughportion of the pulse cycle to determine the diastolic pressure.
 23. Theinvention of claim 22 wherein the pulse cycle chosen comprises the firstpulse cycle of said series of pulse cycles wherein the pulse minimumpoint occurs adjacent to the end of the trough portion, and wherein thediastolic pressure is determined by utilizing the pressure data at thepulse minimum point so chosen.
 24. The method of claim 19 wherein thestep of examining the information stream to determine at least one ofthe systolic, diastolic and mean arterial pressures by selecting atleast one of the two pulse minimum points as a point for determiningsaid at least one of the systolic, diastolic and mean arterial pressuresof the patient includes the step of selecting a pulse cycle in saidseries of pulse cycles wherein the pulse minimum point of the pulsecycle occurs in the middle of the pulse cycle trough portion of thecycle to determine the mean arterial pressure.
 25. The method of claim 1further comprising the steps of providing a data storage means forstoring the information of the data stream and storing the informationof the data stream.
 26. A method of determining mean arterial bloodpressure of a patient comprising the steps of:a. affixing a non-invasivepressure inducing means and transducer means to the patient; b.obtaining a data stream from the transducer means, the data streamincluding pulsation signal data, c. processing said data stream tocreate a generally sinusoidal information stream curve which includespulsation signal data and time data, and has at least one apex point andat least one nadir point, d. determining the patient's systolic anddiastolic pressure, e. creating a scale of arterial pressures by settingthe arterial pressure at the apex point to equal the determined systolicpressure, and setting the arterial pressure at the nadir point to equalthe determined diastolic pressure, f. selecting a pressure determinationpoint in the information stream curve, and g. utilizing the chosenpressure determination point, the scale of arterial pressures and thedetermined systolic and diastolic pressures to determine the patient'smean arterial pressure.
 27. The method of claim 26 wherein the step ofcreating a scale of arterial pressures comprises the step of creatingthe scale by linearly interpolating the arterial pressures.
 28. Themethod of claim 26 wherein the step of selecting the pressuredetermination point comprises the step of selecting a data point in theinformation stream between the apex point and the nadir point, andutilizing arterial pulse pressure at the pressure determination point soselected to determine the mean arterial pressure.
 29. The method ofclaim 26 wherein the step of selecting a data point in the informationstream comprises the step of selecting a pressure determination pointwherein the slope of said information stream curve changessignificantly.
 30. The method of claim 29 wherein the step of selectinga pressure determination point wherein the slope of the informationstream curve changes significantly comprises the step of selecting adata point in the information stream curve wherein the slope increasessignificantly.
 31. The method of claim 29 wherein the step of selectinga pressure determination point wherein the slope of the informationstream curve changes significantly comprises the step of selecting adata point wherein the rate of change of the slope of the curve ismaximized in the interval between said apex point and said nadir point.32. The method of claim 26 wherein the step of selecting a pressuredetermination point in the information stream curve comprises the stepof selecting a pressure determination point in the information streamcurve wherein the rate of change of arterial pressure as a function oftime decreases significantly.
 33. The method of claim 26 wherein thestep of selecting a pressure determination point comprises the step ofselecting a pressure determination point in the information stream curveat a point wherein the pressure exerted on the patient by said pressureinducing means is less than the patient's diastolic pressure.
 34. Anapparatus for determining blood pressure of a patient comprising:a. anon-invasive pressure inducing means and transducer means attachable tothe patient for providing a data stream including pressure data andpulsation signal data, b. an analog to digital convertor means having aresolution of at least about twelve bits, c. processing means cooperablewith the analog to digital convertor means for processing the data tocreate a generally sinusoidal information stream curve of at least onepulse cycle of the patient which correlates the pressure data and thepulsation signal data, the information stream curve being comprised ofat least about one hundred items of pressure data and pulsation signaldata per second, and including a rapidly descending portion, a troughportion, and a rapidly ascending portion, and d. means for analyzing theinformation stream curve trough portion to determine at least one of thesystolic pressure, diastolic pressure, and mean arterial pressure of thepatient.
 35. The apparatus of claim 34 further comprising a graphicdisplay means for graphically displaying the information stream socreated.
 36. The apparatus of claim 35 wherein the graphic display meanscomprises a printer means.
 37. A method of determining the condition ofthe cardiovascular system of a patient comprising the steps of:(a)affixing a non-invasive pressure inducing means and transducer means tothe patient, (b) obtaining a data stream from the transducer meansduring such time as the pressure induced by the pressure inducing meansis at a suprasystolic pressure, the data stream including pulsationsignal data, (c) processing said data stream to create an informationsystem which includes pulsation signal data and time data, (d)processing the information stream to create a first derivative streamwhich includes information relating to the rate of change of the data ofthe information stream, and an integration stream, and (e) examining atleast one of the information stream, first derivative stream andintegration stream at said suprasystolic pressure to determine thecondition of the patient's cardiovascular system.
 38. The method ofclaim 37 further comprising the steps of providing a graphic displaymeans and graphically displaying the information stream as an arterialpulse curve and the first derivative stream as a first derivative curve.39. The method of claim 37 wherein the step of examining at least one ofthe information stream, first derivative stream and integration streamcomprises the step of examining the integration stream to determine thestrength of the heart contraction of the patient.
 40. The method ofclaim 37 wherein the step of examining at least one of the informationstream, first derivative stream and integration stream comprises thestep of detecting the presence of cardiovascular noises by examining thefirst derivative stream.
 41. A method of determining the condition ofthe cardiovascular system of a patient comprising the steps of:(a)affixing a non-invasive pressure inducing means and transducer means tothe patient, (b) obtaining a data stream from the transducer meansduring such time as the pressure induced by the pressure inducing meansis at a sub-diastolic pressure, the data stream including pulsationsignal data, (c) processing said data stream to create an informationstream which includes pulsation signal data and time data, (d)processing the information stream to create a first derivative streamwhich includes information relating to the rate of change of the data ofthe information stream and an integration stream, and (e) examining atleast one of the information stream, first derivative stream andintegration stream at said sub-diastolic pressure to determine thecondition of the patient's cardiovascular system.
 42. The method ofclaim 41 wherein the step of examining at least one of the informationstream, first derivative stream and integration stream comprises thestep of examining the integration stream to determine information aboutthe flow of blood in the circulatory system of the patient.
 43. A methodfor determining mean arterial blood pressure of a patient comprising thesteps of:(a) affixing a non-invasive pressure inducing means andtransducer means to the patient, (b) obtaining a data stream from thetransducer means, the data stream including pulsation signal data, (c)processing said data stream to create an information stream whichincludes pulsation signal data and time data, (d) determining thepatient's systolic and diastolic pressure, (e) selecting a pressuredetermination point in the information stream at a pressure less thanthe patient's determined diastolic pressure, and (f) utilizing theselected pressure determination point, and the determined sytolic anddiastolic pressures to determine the patient's mean arterial pressure.44. A method for determining mean arterial blood pressure of a patientcomprising the steps of:(a) affixing a non-invasive pressure inducingmeans and transducer means to the patient, (b) obtaining a data streamfrom the transducer means, the data stream including pulsation signaldata, (c) processing the data stream to create a generally sinusoidalinformation stream curve which includes pulsation signal data and timedata, and has at least one apex point and at least one nadir point, (d)determining the patient's sytolic and diastolic pressure, (e) selectinga pressure determination point in the information stream curve betweenthe at least one apex point and the at least one nadir point wherein theslope of the information stream curve changes significantly.